Hydrogarbon treatment furfural solvent extraction process



March 8, 1966 R. A. wooDLE ETAL 3.239.456

HYDROGARBON TREATMENT FURFURAL SOLVENT EXTRAGTION PROCESS Filed April 27, 1962 2 Sheets-Sheet 1 March 8, 1966 Filed April 27. 1962 R. A. WOODLE ETAL HYDROCARBON TREATMENT FURFURAL SOLVENT EXTRACTION PROCESS 2 Sheets-Sheet 2 United States Patent O 3,239,456 HYDROCARBON TREATMENT FURFURAL SOLVENT EXTRACTION PROCESS Robert A. Woodle, Nederland, and Paul P. Bozeman, Jr.,

and John I. Nixon, Groves, Tex., assignors to Texaco Inc., New York, N.Y., a corporation of Delaware Filed Apr. 27, 1962, Ser. No. 190,592 9 Claims. (Cl. 208-321) This invention relates to the treatment of liquid hydrocarbon mixtures with a selective solvent. More particularly, it relates to the separation of aromatic hydrocarbons from mixtures with other hydrocarbons by solvent extraction with furfural and an added paraftinic hydrocarbon and distillative separation of the resulting extract-mix with added parainic hydrocarbons. In one embodiment of this invention, alkyl naphthalene hydrocarbons are separated from gas oils by selective solvent extraction with furfural in the presence of a heavy parailinic gasoline fraction and the resulting extract-mix is subjected to azeotropic distillation in the presence of a reflux comprising said heavy paraflinic gasoline fraction.

Gas oils from some aromatic crude sources and gas oils from thermal and catalytic cracking contain substantial quantities of aromatic hydrocarbons, for example, benzenoid, naphthalene and naphthalenic hydrocarbons. This invention is particularly useful in the separation of bicyclic aromatic hydrocarbons from cracked gas oils and distillates having a true boiling range Within the range of 430 to y620 F. These bicyclic aromatic hydrocarbons may be converted to naphthalene by hydrodealkylation of alkyl naphthalenes, or they may be converted to useful chemical products such as phthalic anhydride by oxidation. Naphthalene precursors include alkyl naphthalenes, tetralin or decalin derivatives and generally any hydrocarbon structure containing the basic naphthalene bicyclic ringl These naphthalene precursors are diluted with non-aromatic hydrocarbons, for example, paraflinic and naphthene hydrocarbons of the same boiling range making their separation by simple distillation impossible. It is an object of this invention to provide a means of separating aromatic hydrocarbons useful as naphthalene precursors in concentrated form from mixtures with non-aromatic hydrocarbons. Other objects will be apparent from the following description and claims.

It is well known that aromatic hydrocarbons are highly soluble in furfural and that parainic hydrocarbons are only slightly soluble in furfural so that substantially all of the aromatic hydrocarbons may be extracted from a rafnate comprising non-aromatic hydrocarbons. When it is desired to separate an aromatic fraction of high purity, that is of low non-aromatic content, extraction conditions are selected to achieve maximum selectivity. Selectivity may be increased by employing relatively low extraction temperatures and by employing extract reflux. However, even under highly selective conditions, the extracted hydrocarbon fractions contain some non-aromatic constituents since these non-aromatic hydrocarbons are slightly soluble in the extract-mix. Furthermore, the recovery of high purity aromatic extracts using conditions of high selectivity is usually accomplished only at the expense of a loss in yield of aromatics due to loss of aromatic constituents into the raffinate fractions.

Mice

Substantial increase in the purity of the separated extract may be achieved without loss of aromatics into the raffinate by employing a paranic backwash as a hydrocarbon reux in the extraction step. `By employing a paratlinic backwash stream having a boiling range wholly outside the boiling range of the aromatic feed stock, nonaromatic hydrocarbons boiling within the range of the desired aromatics 4may be displaced from the extract and the parainic backwash which dissolves in the extract-mix may be separated by distillation. In accordance with the process of this invention, a parainic hydrocarbon boiling wholly outside the boiling range of the aromatic feed and separable therefrom by distillation is employed as a backwash, hydrocarbon reux, or re-extraction solvent to reduce the amount of non-aromatic hydrocarbon coboiling with the desired aromatics fraction contained in the extract. The resulting parainic washed extract-mix is then subjected to distillation in the presence of an additional quantity of the paraiiinic backwash hydrocarbon in a distillation step t-o eifect separation of furfural from the extracted aromatic hydrocarbon fraction.

We have found that when using a paraflnic backwash comprising hydrocarbons having at least nine carbon atoms, and boiling at a temperature of at least 250 F, and preferably Within the range of 300 to 350 F. by true -boiling point distillationjt an azeotrope of parainic hydrocarbon and furfural is formed thereby facilitating separation of furfural from the aromatic extract. Such a paraflinic wash oil forms an azeotrope at favorably low oil to furfural ratios and also boils suiciently below the true boiling range `of naphthalene precursor feed stocks to permit easy separation of the paratlinic backwash from the aromatic extract by distillation. Suitable paranic hydrocarbon wash oils may be obtained, for example, by vthe distillative separation of 300 to 350 F. fractions from alkylate or the rainate from the solvent extraction of catalytic reformate.

In the use of a parainic wash-oil in extraction of naphthalene precursor feed stock with furfural, about twothirds of the wash-oil appears in the raffinate and about one-third appears in the extract displacing non-aromatic hydrocarbon coboiling with the extract. That portion of the Wash-oil passing into the raffinate fraction is the most parain acting portion of the wash-oil. By adding additional paraffinic wash-oil into the extract-mix stripper as reflux, sufficient parain is introduced to satisfy the requirements of the azeotrope as well as to increase the concentration of the most parainic acting materials.

An advantage of the process of this invention is that concentrates containing more than percent aromatics may be separated from gas-oil boiling range hydrocarbons with furfural employing moderate extraction temperatures and with moderate solvent rates. Another advantage of the process of this invention is that the solvent is separated from the extract hydrocarbons at relatively low temperatures with a low consumption of utilities.

T'he accompanying drawings diagrammatically illustrate the process of this invention. Although the drawings illustrate arrangements of apparatus in which the process of this invention may be practiced, it is not intended to limit the invention tothe particular materials or True boiling point or true boiling range as used herein refers to a distillation with at least 30 'theoretical plates and at least 5 to 1 reflux ratio.

apparatus described. FIGURE 1 is a iiow diagram of the process of this invention employing common condensation and recovery of the vapors from extract and rafiinate stripping. FIGURE 2 illustrates the process of this invention employing separate 'condensation of the vapors from extract and raflnate stripping and means for purification of the paraiiinic ybackwash oil.

In FIGURE 1, g-as oil feed containing not more than about 1.0 volume percent boiling below 400 F. by true boiling point distillation is introduced through line 1 into treating tower 2. In tre-ating tower 2 of the gas oil feed is countercurrently -contacted with furfural containing about 5 percent water introduced into the top of treating tower 2 through line 3. The furfural dosage may be within the range of about 25 to 250 volume percent of the gas oil feed. Oil phase rises through tower 2 and discharges at a temperature within the range of labout 130 to 170 F. Ias rafnate through line 4. Solvent phase descends in tower 2 and is discharged as extract-mix at a temperature within the range of about 70 to 150 F. through line 5. Intermediate the inlet of gas oil feed line 1 fand extract-mix discharge line 5, a paraflinic backwash is introduced into treating tower 2 through 'line 9 at a rate within the range of about to 100 volume percent of the gas oil feed. Parainic backwash rises through tower 2 and re-extracts non-aromatic constituents dissolved in the solvent phase. Parainic backwash fand -reextracted non-aromatic constituents rise and become a part of :the rafnate phase. A portion of the parainic backwash dissolves in the solvent phase in displacing non-aromatic constituents and passes out with the extractmix in line 5.

Extract-mix in line 5 is discharged to extract stripper 10. Extract stripper 10 may Vbe a conventional distillation tower employing trays, plates or packing and means for reboiling as we-ll known in the art. Stripping may be facilitated lby the introduction of steam in line 11. Reflux comprising paraflinic wash-oil is introduced at the tower top through line 12 to assist in forming an azeotrope and facilitate the separation of furfural. Stripped extract `comprising naphthalene precursors in excess of 90 percent aromatic content is discharged through line 13. Vapors of furfural and parainic wash-oilfare discharged overhead through line 14 to cooler 15 and through line 16 to decanter 17. Condensate in decanter 17 separates into three phases, an oil phase comprising paraffinic wash-oil and a small amount of dissolved water and furfural, a water phase comprising water with a small amount of dissolved hydrocarbon and furfural, vand a furfural phase comprising furfural containing fa small amount of dissolved hydrocarbon and water. The three phases are separated by means of weirs 20` and 21 to permit separate withdrawal from decanter 16. Oil phase is withdrawn through line 9, water phase through line 30 Vand furfural phase is withdrawn through, :line 13.

Raflinate is discharged through line 4 to rainate stripper 25 which, like extract stripper 10, may be a conventional distillation tower. Steam to assist in stripping may be introduced through line 24. Stripped rainate oil, low in aromatic hydrocarbons and useful in the manufac. ture of kerosene and diesel fuel, is discharged through line 27. Light parafnic hydrocarbon from line 9 is introduced through line 28 as reux to the top of stripper 25 to assist in formation of azeotrope and the separation of furfural. Furfural and paraiiinic hydrocarbon vapors are discharged through line 26 and combined with vapors in line 14 for condensation, recovery, 'and recycle.

Water phase separated in decanter 17 resulting from steam condensation as described above, contains some dissolved furfural and oil. These dissolved constituents may be retained in the system by extraction of the water phase with 4a portion of the feed hydrocarbon. Water phase in line 30 is passed to furfural recovery tower 31 in which it is countercurrently contacted with a portion of the gas oil feed introduced through line 32. Water free of dissolved furfural and oil is discharged through line 33 for disposal or reuse. Feed oil containing extracted furfural and oil passes through line 34 and is combined with the gas oil feed passed to treating tower 2. Alternatively dissolved -f-urfural may be recovered from the Water phase by distillation.

In FIGURE 2, a gas oil feed from uid catalytic crack-v ing boiling in the range of about 380 to 530 F. by true Y boiling point distillation is passed ,through line: 51 to treat-v ing tower 52. In tower 52,1'which may 'be a packed column or a rotating .disc contactor or other well known means for liquid-liquid contacting, the ,oil is conntercurrently contacted with furfural introduced through line 53. Hydrocarbon- -phase rising. through the tower discharges as lrainate through line 54. Solvent` phase 4containing dissolved aromatic hydrocarbons passes downwardly and discharges lthrough extract-mix line 55. Light parain s backwash comprising C9 and Cmparaiiinie hydrocarbons -and boiling within the ,range of rabout 300'to 350 F. is introduced into the lower fportion of .tower 52 through line 60. Backwash rising through tower 52 re-extracts a portion of the non-aromatic` constituents and-combines with the raffinate phase discharged through line 54.

Extract-mix from line 55 is passed,toextract-stripper 61 wherein anrazeotrope of parainic hydrocarbons andk Make-up parainic hydrocarbon is introduced into the Vsystem through line 69 and excess parat-iin hydrocanbon is discharged through line70., Furfural solvent is withdrawn through line ,71 and returned to treating tower 52. through line 53. Solvent is withdrawn throughlin'e ;72.

for recovery or purification lnot shown aand make-up vent las necessary is added through line 73.

Rafnate `in line 54is passed to raffinate stripper 75 wherein an azeotrope of parafnic hydrocarbons and furf lfural is `distilled overhead through line 78. Rainate free of furfural and light p-arafiriic hydrocarbon is discharged. through line 76 for use as kerosene, diesel fuel, .or reiined= oil for blending. Stripper 75 is refluxed with light parafnic hydrocarbon through linev 771. Overhead vapors in` line 78' are condensed in cooler 79 and passed through line 80 to decanter 85. Light parainic Vhydrocarbon is withdrawn through line to supply, reux in line 77V and a portion is passed through lines -91 and 92 to supply the lightparafnic backwash in treating tower 52.'

The parafhnic hydrocarbon backwash is separately re'- distilled in parainic oil rerun tower -to prevent the accumulation of hydrocarbons boiling.y near the boiling point of furfural in the system. Light V'parainic hydro-- carbon from extract stripping from line 68 Ais passed through line 101 to parafiin oillrerun tower 100; Separated distillation bottomsboiling above about.350 F. are

withdrawn through line 105; Redistilled paranic hydrocarbon is withdrawn as overhead from tower 100` through Y line 106, condensed in cooler 107, and. passed through line 108 to separator 109. i Rerun paratfrnic hydrocarbon isV withdrawn through linel 115, `a portion is passed to tower 100 through line 116 as reux and remaining redistilled parainic hydrocarbon is passedthrough line 92 and line 60 to treating tower 52.

Example I A light `gas oil from catalytic cracking, is treated in accordance with the process of this invention to separate an aromatic extract sui-table as feedstock for the' manufacture of naphthalene. This gas oil feed is characterized by a gravity of 27.1 API, a total aromatic content of 55.4 volume percent, a refractive index of 1.4894 at 70 C., and a true boiling point distillation as follows:

This gas oil feed is contacted with wet furfural containing 5 percent water at a dosage of 200 volume percent basis charge oil in a rotating disc contacter. Light paraffin backwash at a rate of 50 volume percent of the charge oil is introduced at the bottom of the rotating disc contaCtor. The light paratfinic backwash is characterized by a gravity of 58.6 API, a boiling range of 300 to 350 by true boiling distillation and contains 96.5 volume percent non-aromatic hydrocarbons. Raffinate is withdrawn at a temperature of 150 and extract-mix is withdrawn at a temperature of 120 F.

Extract-mix is charged to an extract stripper operated at a pressure of p.s.i.g., a reboiler liquid temperature of 540 F., a top tower temperature of 332 F. and with an extern-al reflux ratio of vlight parafin to overhead of 0.39. Extract product is withdrawn having a gravity of 13.4 API and containing 92.0 volume percent aromatics. The total aromatic recovery in the extract is 69.6 volume percent of the total aromatics in the feed.

Rafiinate is stripped to produce a refined gas oil fraction having a gravity of 38.3 API, a total aromatics content of 29.1 volume percent and a refractive index of 1.4475 at 70 C.

Example Il The catalytic cracked gas oil of Example I is contacted with wet furfural at a dosage of 100 percent in a solvent extraction tower. A heavy paraffin oil backwash is employed at a dosage of 50 percent of the gas oil feed. The heavy parafnic oil comprises a distillate characterized by a true boiling point distillation wholly above 760 F. at atmospheric pressure, an open cup flash `of 540 F., a gravity of 25.6 API, and a refractive index `of 1.4772 at 70 C. Ral'iinate is separated at 170 F. and extract-mix is separated at 120 F. Extract-mix is distilled in an extractive distillation tower in the presence of an additional 82 volume percent basis extract-mix of heavy paratiinic oil added at the top of the extractive distillation tower. 'Furfural, free of extract oil and heavy parafiinic oil is removed as an overhead product. Extractive distillation bottoms comprising extract hydrocarbons and heavy parafinic oil is redistilled to separate extract hydrocarbons as an overhead fraction. Water Washing the extract hydrocarbon overhead produces an extract product contain-ing 90.2 percent by volume aromatics with an overall recovery of 75 percent of the aromatics in the gas oil feed.

It Will be understood that the contacting of gas oil feed with furfural and the backwash may be effected in the same contacting vessel or that separate contactors may be used for the solvent extraction and the hydrocarbon back- Wash steps. It is also contemplated that furfural in an amount of 10 to 50 percent of the furfural content of the extract mix may be added prior to the backwash to achieve a sharper separation in the subsequent 1re-extraction. It is also contemplated that the backwash may be employed at the same or a different temperature than the furfural extraction step and advantageously higher selectivity may be -achieved by employing a baclrvvash at a lower temperature than the preceding solvent extraction step.

We claim:

1. A method for the separation of an aromatic rich fraction from a liquid hydrocarbon feed mixture having a true boiling range within the range of about 430 to 620 F. comprising aromatic hydrocarbons and non-aromatic hydrocarbons which comprises:

contacting said liquid hydrocarbon feed mixture with a solvent comprising liquid furfural effecting formation of a raffinate phase comprising hydrocarbon and dissolved furfural and an extract-mix phase comprising furfural and dissolved aromatic and nonaromatic hydrocarbons,

contacting said extract-mix phase with a first portion of a parafiinic liquid hydrocarbon mixture having a true boiling range within the range of about 250 to 350 F. effecting displacement of at least a portion of said dissolved non-aromatic hydrocarbons into said rafiinate phase forming a washed extract-mix phase,

and distilling said washed extract-mix phase in the presence of a second portion of said paraffinic liquid hydrocarbon mixture in an amount satisfying the azeotrope of furfural and said parafiinic hydrocarbon.

2. The process of claim 1 wherein the initial true boiling point of said parafiinic liquid hydrocarbon mixture is at least 250 F.

3. The process of claim 1 wherein the true boiling range of said paraffinic liquid hydrocarbon mixture is within the range of 300 to 350 F.

4. The process of claim 1 wherein said additional portion of wash oil is passed as refiux to said distillation zone at a reux ratio of about 0.39.

5. The process of claim 1 wherein said paratiinic liquid hydrocarbon mixture has a true boiling range of at least 50 F. below the true boiling range of said feed oil.

6. In the solvent separation of a feed liquid having a true boiling range within the range of about 430 to 620 F. containing aromatic compounds relatively soluble in furfural and non-aromatic components relatively insoluble in furfural wherein said feed liquid is countercurrently contacted with a solvent comprising furfural in an extraction Zone to form raffinate phase containing non-aromatic components and extract phase rich in aromatic components and containing a minor portion of dissolved nonarornatic components, said extract phase is countercurrently contacted with a first portion of a parafiinic wash oil having a true boiling range within the range of about 250 to 350 F. in a stripping zone effecting displacement of at least a portion of said dissolved non-aromatic cornponents from said extract forming a stripped extract, and said stripped extract is distilled to separate extracted hydrocarbons from solvents, the improvement which comprises distilling said stripped extract in the presence of an added portion of said parafiinic Wash oil in an amount satisfying the azeotrope of furfural and paraffinic wash oil.

7. The process of claim 6 wherein said added portion of said parainic wash oil is employed as at least a part of the reflux in distilling said stripped extract.

8. In the solvent separation of bicyclic aromatic hydrocarbons from a catalytic cracked gas oil having a true boiling range Within the range of about 430 to 620 F. with a solvent comprising furfural wherein said catalytic cracked gas oil is countercurrently contacted with said solvent forming raffinate and extract-mix wherein said extract-mix comprises dissolved bicyclic aromatic hydrocarbons and non-aromatic hydrocarbons, the improvement which comprises:

countercurrently contacting said extract-mix with a first portion of a parafiinic hydrocarbon stream boiling within the range of 250 to 350 F. by true boiling point distillation displacing at least a portion of the dissolved non-aromatic hydrocarbons from rcmaining paraffin Washed extract-mix, and distilling Vsaid parain Washed extract-mix in the presence of a'reux comprising a second portion fof said paranic hydrocarbon in an amount satisfying the azeotrope of furfural and parainic hydrocarbon effecting separation of overhead distillate comprising Y, Y furfural and paranic hydrocarbons and bottoms Y comprising bicyclic aromatic hydrocarbons. v

9. The process of claim 8 wherein said overhead disti1- late is separated into furfural and paratiinic hydrocarbon phases,

at least a portion of said furfural phase is contacted v with said catalytic cracked gas oil,

8: at least a portion of said `parafiiic hydrocarbon phase isredistilled` to a truezboiling end pointsof 350 F., and thus redistilled paratiriic;V hydrocarbon is I contacted with saidrextract-mix. Y v

References Cited bythe Examiner UNITED STATES PATENTS:

5 PAUL M. COUGHLAN,Primary-Examiner.,

ALPHoNso D. sULLIVAmLmmKiner. 

1. A METHOD FOR THE SEPARATION OF AN AROMATIC RICH FRACTION FROM A LIQUID HYDROCARBON FEED MIXTURE HAVING A TRUE BOILING RANGE WITHIN THE RANGE OF ABOUT 430 TO 620* F. COMPRISING AROMATIC HYDROCARBONS AND NON-AROMATIC HYDROCARBONS WHCIH COMPRISES: CONTACTING SAID LIQUID HYDROCARBON FEED MIXTURE WITH A SOLVENT COMPRISING LIQUID FURFURAL EFFECTING FORMATION OF A RAFFINATE PHASE COMPRISING HYDROCARBON AND DISSOLVED FURFURAL AND AN EXTRACT-MIX PHASE COMPRISING FURFURAL AND DISSOLVED AROMATIC AND NONAROMATIC HYDROCARBONS, CONTACTING SAID EXTRACT-MIX PHASE WITH A FIRST PROTION OF A PARAFFINIC LIQUID HYDROCARBON MIXTUE HAVING A TRUE BOILING RANGE WITHIN THE RANGE OF ABOUT 250 TO 350*F. EFFECTING DISPLACEMENT OF AT ELEAST A PORTION OF SAID DISSOLEVED NON-AROMATIC HYDROCARBONS INTOF 